775
ACUS02 KWNS 201727
SWODY2
SPC AC 201725

Day 2 Convective Outlook
NWS Storm Prediction Center Norman OK
1225 PM CDT Fri Sep 20 2024

Valid 211200Z - 221200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
EASTERN NM AND WEST TX...

...SUMMARY...
Scattered severe storms are possible Saturday afternoon to early
evening across parts of the southern High Plains. Isolated strong to
severe thunderstorms are also possible from the mid Missouri Valley
to the Upper Midwest, and also from western Pennsylvania into
northern/central Virginia.

...Southern High Plains vicinity...
A southern stream mid/upper-level low and attendant trough will
progress east across the Four Corners and southern Rockies on
Saturday. Strong southwesterly flow aloft associated with the
ejecting trough will become oriented over eastern NM into the OK/TX
Panhandles by 00z/Sunday. While diurnal heating will result in some
boundary layer mixing, south/southeasterly low-level flow will
result in persistent theta-e advection, and dewpoints from the upper
50s to low 60s F are expected. Steepening midlevel lapse rates will
contribute to modest destabilization, with 1000-1500 J/kg MLCAPE
forecast across parts of eastern NM into the TX Panhandle/South
Plains vicinity. Vertically veering wind profiles amid strengthening
midlevel flow will support supercells, though a tendency toward
increasing storm coverage and redevelopment may result in some
clustering with time. Large hail, sporadic strong/severe gusts, and
a tornado or two are all possible.

Additional strong storms are possible to the north and west across
northern NM into south-central CO beneath the core of mid/upper low.
Instability will be weaker across this area, but isolated strong
gusts and hail will still be possible with the strongest storms.

...Western PA into northern/central VA...
A low-amplitude mid/upper-level shortwave trough is forecast to move
across the Northeast on Saturday. Northwesterly deep-layer flow will
overspread the Upper OH Valley toward the Mid-Atlantic coast. A
corridor of low to mid 60s F dewpoints and pockets of stronger
heating will support weak to locally moderate destabilization.
Modest vertical shear (around 25-30 kt effective shear) will aid in
at least transient organized updrafts. Elongated/straight hodographs
and relatively cool temperatures aloft suggest marginally severe
hail will be possible with the stronger cells. Locally strong gusts
also will be possible where stronger heating and steepening of
low-level lapse rates occurs.

...Central Plains to Mid-MO Valley and Upper Midwest...
The forecast for this region remains quite uncertain for Saturday.
Most guidance depicts ongoing elevated convection across parts of
IA/MO Saturday morning. The evolution of this activity will impact
how the airmass destabilizes/recovers late in the afternoon across
the region. Nevertheless, thunderstorm development may increase
during the afternoon/evening over the Upper Midwest into the mid MO
Valley, as a northern stream upper trough traverses the Canadian
Prairies and the international border vicinity, and an attendant
cold front moves through the region.

In areas that are not overly affected by early-day convection,
diurnal heating and relatively steep midlevel lapse rates atop 60s F
dewpoints will support moderate destabilization, while deep-layer
shear becomes at least marginally supportive of organized storms.
Some guidance suggests a cluster of elevated convection may develop
across Iowa during the morning and intensify as it moves
east-northeastward. Otherwise, isolated storms may develop near the
front during the afternoon, with increasing storm coverage into the
evening. Relatively elongated hodographs will support some hail
potential with the strongest storms, while localized damaging winds
will also be possible, especially if any stronger clusters do evolve
with time.

Farther south, the magnitude of destabilization into central KS
remains uncertain and could be rather limited, though increasing
midlevel flow would support some organized convection if robust
storms can develop. A strong storm or two also cannot be ruled out
with morning convection across MO, and again near any outflow
boundaries during the afternoon/evening. However, confidence remains
quite low regarding storm evolution in this area.

..Dean.. 09/20/2024

$$